import collections
class Solution(object):
    def findTheDifference(self, s, t):
        """
        :type s: str
        :type t: str
        :rtype: str
        """
        c = collections.Counter(t)
        for i in range(len(s)):
            c[s[i]] -= 1
            if c[s[i]] == 0:
                c.pop(s[i])
        return list(c.keys())[0]

data = Solution()
s = "abcd"
t = "abcde"
print(data.findTheDifference(s, t))